1. Field of the Invention
The present invention relates to the reversible immobilization (i.e., attachment) of microbial cells and cell components to solid surfaces through reversible ion-exchange mechanisms.
2. Description of the Prior Art
There are many situations in which intact microbial cells, or cell organelles, or cellular proteins (e.g., enzymes) are of more practical value if they can be immobilized (i.e., attached) on a solid support. Although ion-exchange resins are commercially available for adsorbing organic materials such as microbes and proteins from dilute solutions, the use of such resins results in irreversible binding of lipid-containing materials (such as whole microbial cells and lipoproteins) to the resin. This greatly limits the usefulness and usable lifetimes of such resins.
At neutral pH, cells of different species of bacteria and most proteins have net negative surface charges. Through electrostatic forces, viruses, microbial cells, and anionic proteins can be removed from a suspending medium at neutral pH by use of activated carbon, clay, sand, or anion exchange resins. Although very effective in the removal of biological species, these materials must either be disposed of after use or attempts made to regenerate them by use of concentrated salts, acids or bases. This procedure can be expensive, incomplete, time consuming, and detrimental to the collected species.
U.S. Pat. Nos. 4,832,797 (Vadgama et al.), 4,581,336 (Malloy), 4,572,897 (Amotz et al.), 4,563,425 (Yoshioka et al.), and 4,438,196 (Lantero) describe various techniques for immobilizing enzymes on a substrate. However, none of such patents describes techniques or methods for reversibly binding charged particles on a solid support.
U.S. Pat. No. 4,585,652 (Miller et al.) describes a method for controlled delivery of an ionic bioactive chemical into a physiological medium. The method includes ionically bonding the drug to redox sites within a charged polymer and releasing the drug into the medium by neutralizing the charge on the polymer. The drug molecules are relatively small (molecular weights of a few hundred). This patent does not describe immobilizing relatively large proteins or microbial cells (having molecular weights of several tens of thousands up to a trillion or more) reversibly on the surface of an electrode under a wide range of conditions.
Further, the structure described by Miller et al. involves drug molecules entrapped in the polymer. As a result, there is a diffusion limitation in that the negatively charged drug molecules will either remain entrapped within the polymer matrix (presumably because of steric effects) or they will diffuse slowly out of the polymer.